When it comes to scrummaging, there aren't many more distinguished in the global game than Mike Cron. The All Blacks scrum doctor is recognised worldwide as rugby's ultimate set-piece specialist, the intellectual driving force behind the Kiwi eight with over a quarter of a century spent on the training paddock.

Watching clips of Cron's sessions online, his voice carries the same unchecked enthusiasm whether fine-tuning the world's best or nurturing New Zealand's next batch of all-conquering front-rows.

It's an outlook shared by many of his contemporaries. Talk to Graham Rowntree, Massimo Cuttitta or Greg Feek, and the fondness for a defining feature of rugby that has seen its name dragged through the dirt in recent years burns bright.

They will talk gleefully for hours on end, covering particular set-piece nuances, testing methods, engagement forces and configurations: the elite scrum has become a science, far removed from the grainy footage of years gone by, 16 burly blokes weighed down by slack cotton jerseys, grappling in a vaguely cohesive manner.

But when Cron likens the engagement of his pack to the swing of a golfer, practicing the technique over and over, it becomes clear that scrummaging for the Kiwi is a constant pursuit of perfection.

Cron was a member of the IRB Steering Group that, in tandem with research from Bath University, ushered in the trial changes to the set-piece back in August we now take for granted: the three-step, crouch-bind-set engagement sequence, the added emphasis on a stable scrum, a straighter put-in, and thus, the long-awaited return of hooking at the top level.

These changes were billed primarily as a drive to improve player welfare, with Bath researchers commenting that scrums contributed to a disproportionately high number of injuries (roughly 40% of all catastrophic injuries) relative to the time players spent packing down.

But the IRB were also tasked with addressing the decline of the elite scrummage as a functional, integral and aesthetic aspect of the sport. Statistics from the 2013 Six Nations showed roughly 30% of scrums were reset; while that year's Scotland-Ireland clash at Murrayfield saw the set-piece take up a whopping 21 minutes of game-time.

More recently, as the year-long trial reached its halfway point, awful playing surfaces in Cardiff, Paris and Edinburgh brought front-rows crashing to ground and the faltering scrummage lurching back into the limelight as a blemish on top-class rugby.

Were the law tweaks working? Were players and coaches buying in to the changes? Were we any further forward than we had been a year previous?

"Overall I think we are heading in the right direction," says Cron.

"The stats from the last Six Nations were better, although some games were played on very difficult surfaces for good scrummaging. In some Super Rugby games we are getting outstanding stats. In other games we are at the same level as under the old system."

With images of front-row forwards crouched and poised to crash together like sprinters awaiting the starting pistol now consigned to memory, the short, sharp engagement has been replaced by a new test of endurance.

Cron talks about isometric loading, where packs must, in effect, hold their driving position; stay stronger for longer as the muscles burn, the lactic acid builds and the unyielding exertion takes its toll. It is this that leads to the oft-comical scene of 16 men straining with all their might while the ball sits stubbornly out of reach in the tunnel.

In one recent Super Rugby fixture, adds the scrum doctor, the ball lay untouched in the middle for nearly 13 seconds.

"Talking to the players, particularly the looseheads, they have found a big reduction in stiffness and soreness in the neck and spine after games. There are very few violent collapses like there was under the old system, which must be good," acknowledges Cron.

"But there are now different forces more prevalent, namely isometric loading. By this I mean that under the old system, the total time from the engage until the ball came out was 3.5 seconds (average at the last Word Cup).

"During this time the isometric loading might have been only one second as there was a lot more movement, and quite often the ball was fed while moving forward.

"Under the new system the total time of a scrum has increased. The amount of isometric loading has increased significantly due to the stability. Therefore players at the top level have experienced a lot more loading through their body, in particularly their lower leg.

"I have not noticed any additional injuries, just more soreness in this area. So us coaches have to train our players to adapt to the new forces to prevent injury."

Cron reckons it is now "far easier" for elite referees to make the right calls at scrum-time, for as long as they focus on the big issues rather than the set-piece minutiae.

Indeed, he hopes for a time in the near future where scrum-halves will feed the ball of their own volition, not on the official's command. The IRB are aware of his concerns, but remain fearful that removing the referees' instruction would herald the return of the hit-and-chase, where packs rumble on through the mark before the ball has been fed.

But the Kiwi argues rugby's lawmakers ought to follow the lineout model in widening the channel for delivery, easing the pressure on the hooker who, at present, must perform an impossible act of contortion to reach the mid-line between the two packs.

"I did some testing at the top level and for a hooker to be in a safe pushing position after the set, the distance between the front of his foot and the ball at the middle line was 105 cm," stresses Cron.

"So basically to ask a hooker to hook a ball that is placed in the middle line he has to get himself into an unsafe position and even then would struggle to reach the ball.

"It is fraught with danger to insist that the ball has to be fed down the middle line. The scrum needs to be in line with the lineout. In the lineout the ball just has to be fed anywhere down the inside shoulders of the two lines which are a metre apart.

"I asked the hookers to strike for the ball where they thought they could reach it safely and keep their foot there. The distance between the front of their foot and the middle line was 60 cm; two rugby ball lengths.

"At the moment the law allows one rugby ball length either side of the middle line. This needs to be widened. Recently we had a meeting in relation to this and the referees are allowing the scrum half to stand to the right of centre to allow the feed to be fed in a safe hooking position for the hooker. But the ball must go in straight.

"Anyone who thinks at the top level a hooker can hook the ball from the middle line